1. Field of the Invention
The present invention relates to a valve unit for controlling the flow of a fluid in microfluidic devices, and more particularly, to a valve filler for closing a channel through which a fluid flows and a valve unit including the valve filler.
2. Description of the Related Art
In a microfluidic device designed for performing series of biochemical reactions such as DNA lysis and amplification reactions, a micro-channel forming the flow path for a fluid is formed in a substrate. One of such microfluidic devices is a lab-on-a-chip, where a lysis reaction and a polymerase chain reaction (PCR) can be performed in sequence. The substrate may have a valve unit that contains a valve filler which closes the micro-channel to block the fluid and opens the micro-channel to allow the fluid to flow.
A microvalve unit having a paraffin wax valve filler has been reported. Robin Hui Liu, et al., Anal. Chem., 76 (7), pp. 1824-1831 (2004); Rohit Pal, et al., Anal. Chem., 76 (13), 3740-3748 (2004). According to these references, the valve unit has a block of paraffin that initially closes the channel, and, in order to open the channel, the paraffin is melted using a heater underneath an moved downstream by the pressure from the upstream channel. In such a microfluidic system, however, a large amount of paraffin wax is needed to close the micro-channel, and a large-sized heating member is needed to melt the large amount of paraffin wax, thereby making it difficult to miniaturize and integrate the substrate for biochemical reactions. Also, it takes a long time for the paraffin wax to reach its melting point and it is difficult to precisely control the timing of opening the channel.